A child plays at the Restoration Baptist church in Monrovia, Liberia, on Aug. 31. Liberia said it would deny permission for any crew to disembark from ships at the country's four seaports until the Ebola epidemic was under control.(Photo: Dominique Faget, AFP/Getty Images)

The world is allowing the Ebola outbreak to spin out of control, according to a leading humanitarian group helping to treat patients in West Africa.

In a separate speech, the USA's top public health official also called on global leaders to do far more to control the Ebola outbreak that has now spread to five countries.

"I could not possibly overstate the need for an emergency response," said Thomas Frieden, director of the Centers for Disease Control and Prevention, who just returned from visiting Ebola treatment centers in West Africa. "There is a window of opportunity to tamp this down, but that window is closing. ... We need action now."

Separately, the missionary group SIM USA announced Tuesday that another of its workers, an American doctor, has been diagnosed with Ebola in Liberia.

Although health leaders know how to halt the spread of the virus, "the challenge is to scale it up to the massive levels needed to stop Ebola," CDC's Frieden said, noting, "Speed is key. For every day's delay, it becomes harder to stop it."

Frieden said the Ebola outbreak — the largest in the 40-year-history of the virus — is the first true Ebola epidemic, reaching widely into many countries. In the past, Ebola affected much smaller communities.

The World Health Organization reports that more than 3,000 people have been infected with Ebola in five countries of West Africa — Guinea, Sierra Leone, Liberia, Nigeria and Senegal — and more than half have died.

Ebola now threatens the peace and security of the countries affected, Frieden says, noting that 70 staff from the CDC are now working in West Africa.

"This is not just a problem for Africa," Frieden said. "This is a problem for the world, and the world needs to respond."

Failing to control the virus makes it more likely that Ebola will expand to additional countries, and that Ebola could mutate in ways that make it easier to spread, Frieden said. While the risk of such mutations is low, "it's probably not zero."

Doctors Without Borders, one of the leading humanitarian agencies fighting the epidemic in West Africa, said Tuesday that "the world is losing the battle" to contain Ebola.

"Leaders are failing to come to grips with this transnational threat," said Joanne Liu, president of Doctors Without Borders, in a statement. "States have essentially joined a global coalition of inaction."

The group called on countries with the capacity to handle biological disasters — such as pandemics or bioterrorist attacks — to send more boots on the ground, in the form of trained civilian or military medical teams.

"Funding announcements and the deployment of a few experts do not suffice," Liu said. "The clock is ticking and Ebola is winning. The time for meetings and planning is over. It is now time to act. Every day of inaction means more deaths and the slow collapse of societies."

Doctors Without Borders estimates that its hospital in Monrovia, the capital of Liberia, needs another 800 beds. The hospital now has 160 beds.

"Every day, we have to turn sick people away," said Stefan Liljegren, a Doctors Without Borders coordinator in Liberia, in a statement. "I have had to tell ambulance drivers to call me before they arrive with patients, no matter how unwell they are, since we are often unable to admit them."

Frieden, who visited the Ebola wards himself, said wearing multiple layers of "personal protective equipment" — or moon suits — is "roasting hot" in the tropical climates of West Africa. "Sweat pours down into your goggles and eyes," Frieden says. Doctors wearing two sets of gloves have trouble even drawing blood, he said.

"As bad as the situation is now, everything I've seen suggests that it will get worse," Frieden says.

The World Health Organization last week announced that the Ebola outbreak could grow to 20,000 cases and take another six to nine months to contain.

"In some ways, the most upsetting thing I saw was what I didn't see," Frieden said of his trip to West Africa. "I didn't see enough beds for treatment. One facility with 36 beds, that just opened, had 63 patients. Some were laying on the ground. ... I didn't see data coming in from large parts of the country. I didn't see the rapid response that is needed to keep a single cluster from becoming a large outbreak."

A separate Ebola outbreak is occurring in the Democratic Republic of Congo in central Africa. Tests on the viruses in circulation there show that the outbreak is a "distinct and independent event, with no relationship to the outbreak in West Africa," the World Health Organization said Tuesday.

Health workers unload Martin Salia, a surgeon working in Sierra Leone who had been diagnosed with Ebola, from an ambulance on Nov. 15 at the Nebraska Medical Center in Omaha. (Photo: Sarah Hoffman, AP)

A health worker sprays disinfectant near a mosque after the body of a man suspected of dying from the Ebola virus was washed inside before being buried on Nov. 14 in Bamako, Mali. (Photo: Baba Ahmed, AP)

Health workers with the International Federation of the Red Cross and personnel with Doctors Without Borders take participate in a pre-deployment Ebola training exercise on Oct. 29 at Red Cross headquarters in Geneva, Switzerland. (Photo: Fabrice Coffrini, AFP/Getty Images)

A Kenyan Port Health Services worker tells a boy to return to an observation room for Ebola screening at Jomo Kenyatta International Airport in Nairobi on Oct. 28. (Photo: Daniel Irungu, European Pressphoto Agency)

A photograph provided by attorney Steven Hyman shows nurse Kaci Hickox in an isolation tent on Oct. 26 at University Hospital in Newark, N.J. Hickox was quarantined in New Jersey after caring for Ebola patients in West Africa. She was being released after being symptom-free for 24 hours and will be flown to Maine. She complained that there was not a shower, flushable toilet, television or reading material in the isolation tent. (Photo: Steven Hyman via AP)

Amber Vinson, right, a Texas nurse who contracted Ebola after treating an infected patient, hugs members of her nursing team during a press conference after being released from care at Emory University Hospital in Atlanta. (Photo: Daniel Shirey, Getty Images)

Members of the Community Outreach Team hand out information about Ebola to residents outside an apartment building at 172nd Street and Stratford Avenue in New York. A 5-year-old boy who lives in the building and recently returned to New York City from the West African nation of Guinea is being tested for Ebola after he was rushed to the hospital with symptoms consistent with the disease, according to health officials. (Photo: Don Emmert, AFP/Getty Images)

New York City Police officers stand in front of 546 West 147th Street, the apartment building of Dr. Craig Spencer on Oct. 25. Spencer, who was working in Africa with the Doctors Without Borders organization, was quarantined after showing symptoms of the virus after his return to New York City. (Photo: Bryan Thomas, Getty Images)

Members of the Department of Defense's Ebola Military Medical Support Team dress with protective gear during training at San Antonio Military Medical Centerin San Antonio on Oct. 24. The team will consist of 20 critical care nurses, 5 doctors trained in infectious disease, and 5 trainers in infectious disease protocols. (Photo: Eric Gay, AP)

Members of the media gather in front of the closed Gutter bowling alley, where Craig Spencer bowled recently in Brooklyn, N.Y. Spencer, who tested positive as New York's first case of Ebola, is in isolation at Bellevue Hospital. (Photo: Jewel Samad, AFP/Getty Images)

Health alerts regarding people who may have traveled to particular West African countries are posted in the lobby of Bellevue Hospital in New York. Craig Spencer, a resident of New York City and a member of Doctors Without Borders, was admitted to Bellevue Thursday and has been diagnosed with Ebola. (Photo: Mark Lennihan, AP)

Women work on a protective suit for use in handling people infected with the Ebola virus in a sewing room at Lakeland Industries Inc. Lakeland, a global manufacturer of industrial protective clothing, produces suits to be worm by healthcare workers and others being exposed to Ebola. (Photo: Johannes Eisele, AFP/Getty Images)

Spec. Jason Dumas, left, helps Spec. David Quichocho, right, with his protective boots during a training session at Ft. Carson. Both soldiers are from the 615th Engineer Company, 52nd Engineer Battalion which will be deploying approximately 160 engineers to West Africa to help with the fight against Ebola. (Photo: Jerilee Bennett, The Colorado Springs Gazette via AP)

A Liberian health worker disinfects a street corner where a suspected Ebola patient was picked up and taken into an ambulance to be transported to an Ebola treatment unit in Monrovia, Liberia. (Photo: Ahmed Jallanzo, European PressPhoto Agency)

Health workers from the Liberian Red Cross wear protective gear as they shovel sand which will be used to absorb fluids emitted from the bodies of Ebola victims in front of the ELWA 2 Ebola management center in Monrovia. (Photo: Zoom Dosso, AFP/Getty Images)

German volunteering soldiers wear protective equipment in Appen, Germany, as they take part in an intensive course to prepare volunteer helpers for their deployment in Ebola-hit countries. (Photo: Bodo Marks, AFP/Getty Images)

Doctors and nurses take part in training in treating infectious diseases in an isolation room during a presentation on diagnosing and treating patients with Ebola virus symptoms in Bern, Switzerland, on Oct. 23. (Photo: Alessandro Della Valle, European Pressphoto Agency)

Filipino health workers hold anti-government placards outside a public hospital intended for Ebola patients in Manila. The group criticized the government in its hope of combating and responding to the threat of Ebola, if it hits the country. Placard reads; "The government can't provide sufficient funding for Tuberculosis let alone Ebola." (Photo: Dennis M. Sabangan, european pressphoto agency)

The Taiwanese Centers for Disease Control displays protective gear during a demonstration on how to handle Ebola patients in Taipei, Taiwan. Taiwan has not reported any Ebola infection cases but has designated six hospitals to treat Ebola patients. (Photo: Taiwan CDC via European Pressphoto Agency)

Ashoka Mukpo shakes hands with physician Kristina Bailey after being released from the treatment unit at the Nebraska Medical Center on Oct. 22 in Omaha. Mukpo was treated and released at UNMC after contracting Ebola in West Africa while working as a freelance journalist. (Photo: Taylor Wilson, Nebraska Medicine via Getty Images)

Armed forces of Liberia officer Ew Dennis speaks with community members on Oct. 18 about an Ebola treatment unit to be built in their village. (Photo: Craig Philbrick, U.S. Army via european pressphoto agency)

A health care worker in protective gear sprays disinfectant around the house of a person suspected to have Ebola virus in Port Loko Community, on the outskirts of Freetown, Sierra Leone. (Photo: Michael Duff, AP)

British Army medics board an airplane as they depart for Sierra Leone at RAF Brize Norton in Brize Norton, England. They will man the Ebola Training Academy, instructing the health care workers who will be working in the five Ebola Treatment Units the UK is currently building. (Photo: Matt Cardy, Getty Images)

Barbara Smith, left, a nurse at Mount Sinai Health Systems, and Dr. Bryan Christiansen, a member of the Center for Disease Control and Prevention's Infection Control Team for the Ebola Response, demonstrate proper safety techniques during an Ebola education session for healthcare workers at the Jacobs Javits Center on Oct. 21 in New York. (Photo: Timothy A. Clary, AFP/Getty Images)

British military medics wait at a departure lounge before boarding an aircraft for Sierra Leone at Royal Air Force base Brize Norton in England. The medics from 35 Squadron, 5th Medical Regiment, will staff the Ebola Training Academy, instructing health care workers who will be working at five treatment units. (Photo: Matt Cardy, Getty Images)

Passengers leave the Carnival Magic after docking in Galveston. A Dallas lab supervisor who handled a specimen from Thomas Eric Duncan, who died last week after contracting Ebola, was in voluntary isolation in her cabin aboard the cruise ship. She tested negative. (Photo: Jennifer Reynolds, AP)

Men in hazmat suits clean the station where a person became sick at a DART train station in Dallas on Oct. 18. The person had supposedly been at the same apartment complex where Ebola patient Thomas Eric Duncan was staying. (Photo: Larry W. Smith, European Pressphoto Agency)

A health worker takes a baby from his mother as he prepares to carry the infant to a reopened Ebola holding center on Oct. 17 in the West Point neighborhood in Monrovia, Liberia. The baby, his mother and grandmother were all taken to the Ebola center after they tested positive for a fever. (Photo: John Moore, Getty Images)

An Ebola tracing coordinator checks the temperature of Jessica Sompon and discovers she has a fever in the West Point neighborhood in Monrovia. A family member living in the home died the previous day from Ebola. (Photo: John Moore, Getty Images)

A custodial worker leaves after cleaning Davis Elementary School in Dallas, Texas. The school was closed after it was discovered that a health care worker who treated one of the Texas Health Presbyterian Hospital nurses infected with the Ebola virus lives at a home with students from the school. (Photo: Chip Somodevilla, Getty Images)

Employees with Cleaning Guys Environmental carry disinfecting equipment into North Belton Middle School. The Central Texas school district has temporarily closed three of its campuses after a family of four, including two students from the district, traveled on the same flight as a nurse who has since been diagnosed with Ebola. (Photo: Rusty Schramm, The Temple Daily Telegram, via AP)

An ambulance carrying Texas Health Presbyterian Hospital nurse Nina Pham leaves the Frederick Municipal Airport on Oct. 16 in Frederick, Md. Pham contracted Ebola when she was part of a team who cared for Thomas Eric Duncan, a Liberian man who eventually died from the virus on Oct. 8. (Photo: Mark Wilson, Getty Images)

People for a convoy transporting Texas nurse Nina Pham after she arrived at Frederick Municipal Airport on Oct. 16 in Frederick, Md. Pham was moved to the National Institutes of Health facility in Bethesda, Md. (Photo: Patrick Semansky, AP)

Hospital staffers cheer as an ambulance transporting nurse Nina Pham, who is infected with Ebola, leaves Texas Health Presbyterian Hospital for Love Field in Dallas. Dozens of co-workers gathered outside the hospital and waved signs in support as Pham was flown to a health care facility in Maryland for treatment. (Photo: G.J. McCarthy, The Dallas Morning News, via AP)

After putting on their protective gear, hazmat workers on Oct. 16 prepare to enter the apartment at The Village Bend East complex where a second health care worker who has tested positive for the Ebola virus resides, in Dallas. Nurse Amber Vinson joins Nina Pham as health workers who have contracted the Ebola virus at Texas Heath Presbyterian Hospital while treating patient Thomas Eric Duncan, who has since died. (Photo: Mike Stone, Getty Images)

Hazmat workers with Protect Environmental unload barrels in preparation for decontaminating an apartment at The Village Bend East apartment complex where Amber Vinson, a second health care worker who has tested positive for the Ebola virus, resides in Dallas. (Photo: Mike Stone, Getty Images)

Members of the Dallas Fire-Rescue Haz Mat Unit tapes off the door of a second health care worker who tested positive for the Ebola virus on Oct. 15 at the The Village Bend East apartments in Dallas. The worker at Texas Health Presbyterian Hospital was monitoring herself for symptoms and reported a fever. She was in isolation within 90 minutes. (Photo: Sana Syed, City of Dallas, via AP)

Heinz Schuhmacher, left, and Marc Dangel, advisers for infection prevention, show how to properly put on protective garments during a demonstration on how to handle Ebola cases at the university hospital in Basel, Switzerland. The World Health Organization projects the Ebola infection rates in West Africa will rise to 5,000 to10,000 new cases a week by December. (Photo: Ennio Leanza, European Pressphoto Agency)

Aid workers from the Liberian Medical Renaissance League stage an Ebola awareness event in Monrovia, Liberia. The group performs street dramas to educate the public on Ebola symptoms and the handling of people who are infected with the virus. (Photo: John Moore, Getty Images)